1942 mauser luger

[cwckac]

i have a 1942 luger with a sear safety, it has the mauser banner.at the back of the pistol there is a u , what would this mean. also on my clip it has the same serial no as the gun. but it also has po8 and fxo with three lines under it and the no 37 under the three line. any info would be appreciated. thank you chuck